The present invention relates to a triode-structure fluorescent display device which uses an electron-emitting source comprising a carbon nanotube.
A field emission type electron-emitting source using carbon nanotubes attracts attention as an electron-emitting source for a fluorescent display device such as an FED (Field Emission Display) or vacuum fluorescent display. In a carbon nanotube, a graphite single layer closes cylindrically, and a 5-membered ring is formed at the distal end of the cylinder. Since the carbon nanotube has a typical diameter of as very small as 10 nm to 50 nm, upon application of an electric field of about 100 V, it can field-emit electrons from its distal end. Carbon nanotubes include those with a single-layered structure described above and those with a coaxial multilayered structure in which a plurality of graphite layers stack to form a telescopic structure and each graphite layer closes cylindrically. Either type can be used to form an electron-emitting source (see U.S. Pat. No. 6,522,055).
A field emission type electron-emitting source using conventional typical carbon nanotubes comprises a flat substrate electrode in which many carbon nanotubes are arranged. By applying a high voltage across the substrate electrode and an electron extracting electrode opposing it, the electric field is concentrated to the distal ends of the carbon nanotubes to emit electrons from them. A method of manufacturing such an electron-emitting source includes, as is known well, one that uses a substrate made of a metal including iron or nickel and forms a film formed of carbon nanotubes on the surface of the substrate and the wall of a through hole wall in accordance with thermal CVD (Chemical Vapor Deposition). When manufacturing carbon nanotubes according to this method, the electron emission uniformity improves, and a state in which a chain of destructive phenomena due to local field concentration does not easily occur can be obtained.
As a fluorescent display device which uses such an electron-emitting source, a triode-structure FED (flat panel display) shown in FIG. 4A has been proposed (see Japanese patent Laid-Open No. 2002-343281). This flat panel display comprises a glass substrate 401 and a translucent front glass 408 arranged to oppose the glass substrate 401. The two end faces of a frame-like spacer glass (not shown) adhere to the peripheral portions of the glass substrate 401 and front glass 408 through low-melting frit glass. The glass substrate 401, the front glass 408, and the spacer glass form an envelope. The interior of the envelope is maintained at a vacuum degree on the order of 10−5 Pa.
A plurality of substrate ribs 402 standing vertically to be parallel to each other are disposed on the glass substrate 401. Electron-emitting sources 403 are disposed on the glass substrate 401 sandwiched by the substrate ribs 402. As shown in FIG. 4B, each electron-emitting source 403 comprises an electrode portion 431 serving as a cathode, and an electron-emitting layer 432 formed on the surface of the electrode portion 431. The electron-emitting layer 432 comprises carbon nanotubes which are formed on the surface of the electrode portion 431, made of an alloy of iron, nickel, or the like, by CVD using a carbon source gas such as methane or carbon monoxide. In the electron-emitting layer 432, a plurality of fibrous carbon nanotubes entangle each other to form a cotton-like layer with a thickness of about 5 μm to 50 μm.
Each electron-emitting source 403 (electrode portion 431) forms a strip-like shape extending in the same direction as the substrate ribs 402, and includes openings at predetermined intervals. In other words, each electron-emitting source 403 forms a ladder-like shape. A plurality of electron extracting electrodes 404 extend on the substrate ribs 402 in a direction perpendicular to the substrate ribs 402. The plurality of electron extracting electrodes 404 are arranged at predetermined intervals in a direction perpendicular to the substrate ribs 402. Each electron extracting electrode 404 has electron-passing holes 404a at predetermined intervals to form a ladder-like shape.
Front ribs 405, extending in a direction perpendicular to the substrate ribs 402 and standing vertically to be parallel to each other, are formed on the substrate ribs 402. In the envelope, the front glass 408 is supported on the substrate ribs 402 through the front ribs 405. The front ribs 405 are disposed on the substrate ribs 402 at gaps to correspond to the electron extracting electrodes 404. In other words, on the substrate ribs 402, the electron extracting electrodes 404 are disposed each between the two adjacent front ribs 405.
Phosphor layers 407R, 407G, and 407B, and metal-backed films 406 which serve as anodes to cover the phosphor layers 407R, 407G, and 407B, stack on the inner surface of the envelope of the front glass 408. On the inner surface of the envelope of the front glass 408, the phosphor layers 407R, 407G, and 407B are sequentially arranged each between the two adjacent front ribs 405. The phosphor layer 407R comprises a red-emitting phosphor. The phosphor layer 407G comprises a green-emitting phosphor. The phosphor layer 407B comprises a blue-emitting phosphor.
In the flat panel display having the above arrangement, a predetermined potential difference is applied between the electron extracting electrodes 404 and electron-emitting sources 403 such that the electron extracting electrodes 404 side has a positive potential. This extracts electrons from the distal ends of the carbon nanotubes that form the electron-emitting layers 432 at regions where the electron extracting electrodes 404 and electron-emitting sources 403 intersect, and the extracted electrons are emitted from the rectangular electron-passing holes 404a of the electron extracting electrodes 404. At this time, if a positive voltage (acceleration voltage) is applied to the metal-backed films 406, it accelerates the electrons emitted from the electron-passing holes 404a toward the metal-backed films 406. The accelerated electrons are transmitted through the metal-backed films 406 and bombard the phosphor layers 407R, 407G, and 407B to cause them to emit light.
For example, with the metal-backed films 406 being applied with a positive voltage and a predetermined electron-emitting source 403 being applied with a predetermined negative voltage, assume that a positive voltage is applied to a predetermined electron extracting electrode 404. This can selectively cause any one of the phosphor layers 407R, 407G, and 407B, which corresponds to a portion where the row of the electron-emitting source 403 applied with the negative voltage and the column of the electron extracting electrode 404 applied with the positive voltage intersect, to emit light. The intersecting portion described above corresponds to one display dot of the flat panel display.
In the conventional flat panel display described above, an abnormal dot may be present which constantly emits light even when it is not selected, and some electron-emitting source 403 (electrode portion 431) may vibrate during operation to generate abnormal noise. These problems arise due to the following factors. During the operation, an electric field from an electron extracting electrode 404 applied with the voltage causes the corresponding electron-emitting layer 432 to emit electrons. Some of the emitted electrons may accumulate on the surface of the glass substrate 401 to charge it.